Why Pentium chips still rule space

Space exploration: The computers that power man's conquest of the stars

Excerpts:

To this day, Nasa still uses elements of technology that powered the moon landings of the 1960s and 1970s, while the International Space Station (ISS) - the manned station circling the Earth 250 miles above our heads - relies on processors dating back more than two decades.

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When it comes to spacecraft, design reliability - and not bleeding edge technology - is the watchword, with onboard chips having to undergo extensive testing to prove their robustness and compatibility with the spacecraft's onboard software.

Each of its computer chips has to be "hardened" to protect it from the high-energy radiation that permeates outer space, a complex process that means the newest processors are almost never used onboard spacecraft.

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Just speccing out and procuring the three Pentium chips for the upgrade has taken years, due to budgetary constraints and the need to design the hardware to minimise conflicts with the onboard system software.

"The challenge is trying to build new technology that looks like the old technology - you don't want to impact the software so it has to look as much like the old hardware as possible," said David Pruett, a former software and computer system manager for the space station who now works for Nasa contractor GeoControl Systems.

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According to Dr Norman Kluksdahl, systems engineer with the mission operations facilities division at Nasa mission control, upgrades must be performed in parallel with the normal station operation.

"Then we have to seamlessly hand over [from the old software to the new software]," he told silicon.com. "I would equate it to driving your car down the road at 80km an hour and changing the tyre while you're moving."

To avoid any unwanted surprises, every new software revision goes through two and a half years of development, planning and testing before being uploaded to the station.

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Due to the complex and costly nature of upgrading ground control systems in ESOC, ESA will sometimes run an entire satellite mission - which can last several years - without performing an upgrade to the original hardware, OS or applications.

Consequently ESOC runs computers of varying ages, with the oldest machines dating back at least 15 years, with ESOC staff having to support these legacy machines alongside the modern HP workstations used to control the newer satellite missions.

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Maintaining such aged hardware unsurprisingly brings challenges such as getting hold of spares to repair computers that are no longer being made or finding staff with the skills needed to maintain software written in old languages.

"You have a problem with the availability of expertise: to find a good Fortran programmer or someone that can work on the VMS [Virtual Memory System] OS is not easy today - you don't find many young people who want to do that," Merri said.

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Today Mission Control Center has 550 workstations linked to 150 servers running 23 different sub-systems.

Since 1996, Nasa has used standardised Unix workstations in both the shuttle and space station flight control rooms, which system engineer Kluksdahl said has greatly simplified their running.

Before the 1996 revamp the flight control rooms relied upon a patchwork of incompatible computer hardware of varying ages, which needed custom-built interfaces to get them to work together.

"If you replaced one piece of it, you either had to redevelop the old interface [between the machines in the flight control room] for the new hardware or you had to replace the whole building at once.

"Because the machines were obsolete, procuring spare parts was difficult and it became almost impossible," Kluksdahl said, adding that Nasa staff had to hunt out spare parts on the second-hand computer market.

Comment: The simplicity of the Apollo computer is interesting. A simulator of the Eagle lander is available for XP